The problem of tax evasion by passing custody markers is a major problem in many countries. In the U.S.A., a colored dye is added to diesel to visually identify the fuel for tax-exempt use in off-road situations. The colored diesel is exempt from federal taxes, principally because the main purpose of the tax is for the funds to be used in highway development and maintenance. However, the coloring agent may be removed by relatively simple methods such as acid/base reactions. The coloring agent is often removed because it is profitable to remove the coloring agent and use the tax-exempt fuel in on-road vehicles.
What is needed is a chemical that can be co-added with the colored dye, and provides a more secure technique for the field determination of the presence of the dyed product. The chemical should not be easily removed using simple methods. Also, it would be beneficial if no sample preparation of the compound is required, little training of the monitoring personnel is required, and the chemicals used for marking or tagging the fuel were relatively inexpensive and could be used either singly or in combinations to provide a number of distinctly different marker sets.